Composition and use thereof for removal of deposits from a metal surface

ABSTRACT

Deposits are removed effectively from a metal surface to which they are adhering by contacting such solids with a composition comprising by weight of from about 1 to about 6 percent CrO3, from about 38 to about 60 percent H2SO4, and balance substantially water, to solubilize the deposits and removing the so used composition containing solubilized deposits.

United States Patent Inventors Theodore E. Maiewski;

Arthur .1. Pastor, both of Midland, Mich. Appl. No. 788,654 Filed Jan. 2, 1969 Patented Oct. 26, 1971 Assignee The Dow Chemical Company Midland, Mich.

COMPOSITION AND USE THEREOF FOR REMOVAL OF DEPOSITS FROM A METAL SURFACE 8 Claims, No Drawings U.S. Cl 134/3,

l34/35; 134/41, 252/87 Int. Cl C23g 1/02 Field of Search 252/80,

Primary Examiner-Leon D. Rosdol Assistant Examiner-William E. Schulz AttorneysGriswold & Burdick and Charles W. Carlin ABSTRACT: Deposits are removed effectively from a metal surface to which they are adhering by contacting such solids with a composition comprising by weight of from about I to about 6 percent CrO; from about 38 to about 60 percent H 80 and balance substantially water, to solubilize the deposits and removing the so used composition containing solubilized deposits.

COMPOSITION AND USE THEREOF FOR REMOVAL OF DEPOSITS FROM A METAL SURFACE BACKGROUND OF THE INVENTION The invention relates to ,the removal of difficulty soluble, more-or-less tenaciously adhering solids, varying in consistency and hardness, comprising incrustations, scale, gummy or greasy accumulations and the like including either or both organic and/or inorganic materials and particularly mixtures thereof from metal surfaces. The surface to which the invention specifically relates is that found on the inside of heat exchangers, steamboilers (including both the coils or tubes and the shell) and most especially the tubes, shells, and transfer lines and vessels through which fluids being treated and temperature-conditioning fluids pass in refinery equip-. ment. Such equipment, because of its intricate design and the nature of the accumulated scale and due to the desire to remove such scale at or near operating temperatures during a minumum of down time and without the need to use techniques requiring abrasive materials or mechanical devices, makes meeting the need for an effective chemical cleaning process for such equipment especially important.

Great difficulties have been encountered in attempting to remove adhering solids commonly associated with refinery equipment because the carbonaceous and hydrocarbonaceous organic materials are often intimately associated with inorganic materials which combination is exceedingly resistant to solubilization by any known composition. Many of the units of such refinery equipment needing cleaning are located at difficulty accessible places and cannot practically be dismantled and cleaned by abrasive or jet means. For example, a usually effective remover of such deposits, viz, a nitrosyl sulfuric acid and sulfuric acid mixture, is not satisfactory because, although it attacks the organic materials, it does not attack the inorganic. Nitric acid compositionsare not acceptable because an adequate inhibitor of the corrosivity nitric acid on metals is not know. Hydrochloric acid does not adequately attack the organic materials in the scale. In fact, heretofore, certain cokelike nd polymeric deposits in refineries have resisted effective solublization by any known chemical agent.

SUMARY THE INVENTION The invention provides a composition which when used ini accordance with the method of the invention safely and effectively solubilizes scale of the nature above described at tem g peratures between about 125 F. and about 300 F. and; preferably between about 150 F. and 250 F. Some benefit is obtained within a few minutes by the practice of the invention, but it is recommended that the time for treatment be at least about 0.5hour. It may require as long as 6hours in severe cases.

The invention is (l) a composition comprising by weight between about land about 6percent of CrO between about 38 and about 60percent of H,SO ,and enough water to make lpercent and (2) the method of removing adhering deposits from ferrous metal surfaces, (an alloy comprising at least, about SOpercent iron) particularly from carbon steel surfaces; (e.g. AlSl lOlOor l020)employing said composition. For; practical use, the composition used in the invention seldomi contains less than about Bpercent Cro and seldom contains} more than about 57percent H,S0 All percentage composi-{ tions to which reference are made herein are per cent by weight. r

Cro is commonly referred to as chromic trioxide or chromic acid. If preferred it may be found in situ in the aque-, ous H,S0,(as by adding dichromate compound which decom-= poses in H,SO yielding CrO,) but no advantage is seen by following such procedure since CrO,is a stable solid powder. It is understood, however, that the invention covers an embodiment wherein the CrO,is formed in situ. e

PRACTICE OF THE INVENTION the danger of corrosion is thereby lessened. On the other hand, the H,SO is preferably below about 55 percent because at higher concentrations than that, it is less effective than desired to remove the adhering solids particularly because insufficient Cro dissolves in appreciably higher H,SO concentrations. Accordingly, between about 47percent and about 55percent H,S0 is most commonly used. For practical purposes, the concentration of CrO,and of 11,80. should be such as to provide enough CrO to show insufficient corrosion to be objectionable and on the other hand, enough H,SO should be present to remove the deposits. The highest limit of CrO is that which dissolves in the selected concentration of ",SO, in water. For example, in a 52percent to 53percent H solution, not more than about Spercent CrO,will dissolve at 200 F. If the concentration of H,SO is greater than about 60percent it is not possible to dissolve as much as 3percent CrO, For practical operation according to the invention the l-l,SO concentration is high enough to remove the adhering deposits but yet not so high that enough CrO,cannot be dissolved to provide adequate protection to the ferrous metal being treated.

4 ln summation, the following amounts of CrO 3 an,H,SOin percent by weight and balance water may be employed in the practice of the invention The invention may be practiced by employing any convenient and available mixer to prepare the composition. The components of the composition, within the specified proportions are readily miscible to prepare a stable composition.

To clean a tubing, transfer line, storage tank, heat exchanger shell, or the like, hereinafter referred to usually as a vessel, the composition is preferably heated to at least l50 but preferably not over abut 250 F. and pumped through the vessel having scale on the interior thereof to be removed or, alternatively in the case of a small vessel immersing the vessel in the cleaning composition, so that the cleaning composition is brought into contact with the deposits to be removed and such contact maintained for at least about 0.5hour during which time the deposits are subjected to a soaking process.

' Some agitation during the soaking period is often helpful but is SERIES ONE The percent organic material in the six different samples was obtained by ignition loss and were found to be the values 1 shown in table I.

TABLE I Ei6ii 4 ignition Loss of Deposit Deposit Number rganic Content by weight SERIES TWO 1n each'six 250milliliter beakers as placed 1 gram each the six different deposits to make a total of 36' tests. To each beaker, containing the one-gram sample of the untreated deposits were added l50milliliters of a solution containing Spercent of cro dissolved in aqueous solutions of 11,80 of varyingconcentrations each of the six solutions (of each the six sets of tests) being increased by l0percent from i0percent in thefirst test to ,60percent in the sixth test. Theresulting ac-. tualpercent by weight of each of CrO ll,SQ and ",0 are also set out in the tableil, infra. Each of the 36beakers was then covered with a watch glass, placed in an oil bath at I75 F. and retained therein for 6 hours. At the end that time, the" solutionsstill at 175 F; were filtered on a preweighted coarse -60 -milliliter sintered glass Buchner funnel. The residue was collected on the filter and washed bypassing a measured quantity of water therethrough until no color remained. The amount of water required for each sample to attain this end was 200milliliters. The; tunnel containing the residue was placed in an oven at 200F., retained therein for l6hours, and thereafter removed therefrom, cooled to room temperature, and weighed. The total weight so obtained was subtracted from the original (funnel plus residue) weight and the resulting difference divided by the original weight, the quotient so. calculated was the fraction (which when multiplied by. l00percent gave the percent of deposit which had gone intd solution. The results are shown in table 11. i

SERIES THREE The procedure of Series Two was repeated except that the temperature of the oil bath into which the beaker containing the samples of deposits and treating solutions were placed and maintained for 6 hours as 200 F. The percents of deposit dis solved in thisseries are shown in table ili.

TABLE II Series Two-Deposits treated for 6 hours at 176 F. with composition of the invention Percent by Weight oi Deposits Treating Solution Used Disso ved TABLE III Series Three-Deposits treated for 6 hours at 200 F. with composition I of the invention Percent by Weight oi Deposits Treating Solution Used Disso ved 5 by wei ht Resultin per- CZO; disso ved 1 cent by eight in aqueous compositiim i 2 3 4 6 6 4.8 CFO: 19. H2504 20%H2SO4.-.-. 76. QHIO 83.1 78.8 83.1 74.2 89.6. 85.5

, 4.8 CF03 3071180 {g fl g }886 752 886 714 921 875 I 4--- 2 4.89 (Jroi H2304"..- 57.1 oHsO 95.2 100.0 97.6 68.5 96.6 89.0

4.8 CrO; 47.6 0 H3804 50%H2SO4 47.6 HzO 99.5 100.0 96.9 72.0 98.9 90.8

1 Due to the higher concentration of H1804, not all of the CrO; went into solution. W

By reference to tables ii and Ill it can be seen that the most effective concentration of H,S0in water employ, with which Spercent by weight CrO,has been admixed, is 60 percent and that the least effective concentration of H, 80, in 'water'there shown is 60 percent. The tables show that amounts of H, S05 down to i0percent are very effective, but, as will be shown subsequently-amounts less than about 38percent 11,80, are

not used because corrosivity then becomes a problem.

scales FOUR Additional Sto IOgram untreated portions of each of the six types deposits identified above by number i through 6 were :weighed and each slurried several times in 25-ml. portions of carbon tetrachloride to extract any organic components jtherefrom. The slurries were then filtered, whereby the ex- ;tracted organic components passed out in the carbon ;tetrachloride filtrate and the inorganic components remained analysis. The results of the various tests of each de o it are set out below in terms of the percentage range obtained for each s21er 9.- q

. X-RAY ANALYSES OF HEAT EXCHANGE DEPOSIT FROM 5% by Wei ht Resulting per- CrO disso ved cent by weight 4 in aqueouscomposition 1 2 3 4 5 6 9.5% H280 10% H280 85.7% H 0 80. 1 63. 5 74. 0 62. 6 64. 6 78.5

4.37 CPO; 19.3%. H1504 20%H2S0 76. a a 84.3 74.5 82.6 67.6 79.1 84.1

i 4.87 CPD: 28.5 0 H280 %HzSO 06. Hi0 84.3 76.0 86.3 64.1 89.5 86.7

0 01'03 .1 H280 40% H280 57.1 0 H4O 85.5 89.0 68.2 93.5 85.9 10

4.8 9 0103 47.5 0 H480 50% 11180 47.6 H2O 99.8 100.0 94.7 69.4 96. 9' 93.1

4.8 CrO; 57.1 0 H280 607 11280 38.1 1120 58.2 71.2 54.7 62.0 88.8 38.8

4.5 a cron I Due to high concentration of H not all the C10 went into solution. 7 g

WHI H THE ORGANIC EXTRACTED BY 0014 TABLE IV.-SE RIES FOUR COMPONENTS HAVE BEEN Deposit No. 2, obtained irom shell side oi heat exchanger at a catalytic cracker Goethite as a- Fe00H Pyrrhotite'as Fer-x8... Hematite m Fe40;.

Deposit No. 4, obtained from shell side of heat exchanger lrom catlaytle cracker Iyrrotite as Fol-XS 20 Pyrite as FeSz 10-20 Quartz as SiO:

Deposit No. 5, obtained from shell side of a heat exchanger of a catalytic cracker Magnetlte as F0304 40 Hematite as F020; -20 Iyrrhotite as Fer-XS. 30-40 Quartz as SiOz 5 Iron 5 Deposit No. 0, obtained from shell side ol a catalytic cracker l'yrilo as FtSz 40-50 lyrrhotite its Fer-XS 30 .\l:\rensli\-ns Fess 10-20 l'vl'i'lcfvrrne 'nnite ns Fe4[Fe(CN)a]s 10-20 Referenceto the analyses of the portions ofthedeposits, not soluble in carbon tetrachloride as set out above showathe presence of high proportionsof components ofvery'difiiculty removable deposits.

SERIES FIVE The following tests were conducted (not in accordance with the invention) for comparative purposes. They were conducted similarly to the procedures followed above exceptthat only one of the two essential ingredientsin the aqueous composition required by the practice the invention was present.

Table YrQ m Series Eive Effect of Sulfuric Acid or Chromic Acid Alone on Deposits; Deposits Treated for 6 Hours at-200 F. Percentage of Deposit Dissolved in Treating Solution Treating Deposit Numbers Solution l 2 3 4 5 6 in water 46.8 50.7 46.8 60.7 30.8 58.8 Con. H,SO 68.6 66.0 67.0 44.2 23.3 34.8 50% H,SO, 65.8 63.5 67.l 40.8 53.l 34.9 80% H,SO, 45.5 5l.7 59.0 42.3 4|.8 33.0 80% I-I 40.l 32.3 42.6 42.4 45.8 23.9 l.7% CrO,

This was the maximum amount of C10, that could be dissolved in 80% aqueous H,S0,.

Table V shows were where either 00 or H 80 alone is dissolved in water and used in attempts to solubilize actual refinery equipment deposits, the results are unsatisfactory Accordingly, both components are essential to attain the objec-, tives of the practice of the invention as shown in tables II and:

III.

SERIES SIX TABLE VI Concentration of H,S0. in water containing 5% by Corrosion Rate weight .CtO, lb.lft.lday

l0% I7.l 20% 25. 2o.2 25.9 42. 1: 2.9 42.85% 2.3 43.67% 0.0032 '44.l0 0.0006 45.20 0.0025 47.30 0.0004 49.57 0.0005 49.94 0.0005 5 I .2l 0.004] 52.74 0.0048 53.88 0.0063 54.51 0.0052

Reference to table VI shows that the rate of corrosion drops off precipitouslywhen the percent of H 80 is increasedto about42'percent in the presence-of CrO when the concentration of H,SO -is further increased without dropping the percent of -Cr0;,.appreciably, the rate of corrosion continues to remain very low and well within the acceptable amount for the length of contact which is necessary for removal of scale or other accumulated deposits from a ferrous metal surface in practical operations.

SERIES SEVEN TABLE VII 1: CrO, by weight Deposit No. 2 Dissolved Reference to table VII shows that the presence of only one percent Cr; is adequate but that 5 percent thereof appears optimum in a 50 percent H solution for dissolving refinerytype scale.

SERIES EIGHT This series of tests was conducted to show the effect of varying times of contact of the descaling solution of the invention with scale which is representative of that which forms on ferrous metal industrial equipment.

l Gram of No. 2 deposit (as above defined) was placed in ISO ml. of a 47.6 percent H 80 percent, 47.6 percent water, 4.8 percent CrO by weight solution at 200 F. and retained'at that temperature for 6 hours. At hour intervals the percent scale dissolved was ascertained. The results are shown in table VIII.

TABLE VIII Time in Hours Scale Deposits Dissolved mil-aun- Reference to table Vlll shows that excellent results are obtained in 1 hour and complete dissolution the scale occurred in 6 hours. By extrapolation, it is obvious that an appreciable amount of accumulated deposits are dissolved in less than an hour, e.g. in 0.5 hour.

SERIES NINE The above tests were repeated at l75 F. with comparable I results showing but only a slightly slower rate of dissolution.

Having Described out Invention, what we claim and desire to protect by Letters Patent is:

l. A method for removing tenaceously adhering solids composed of organic and inorganic substances from ferrous metal surfaces which involves contacting the solid substances with an aqueous solution consisting essentially of a weight basis from I to 6 CrO and from about 42 percent to 60 percent H 80. while maintaining the temperature of the composition between about I25 F. and 300 F.

2. The method of claim I wherein the Cro is present in an ant between about 3.5 and the point of saturation and the H is present in an amount between abut 40 an 57.0 percent.

3. The method of claim 1 herein the CrO is present in an aunt at least about 3.5 percent and the H 80 is present in an amount of between about 47 percent and 55 percent.

4. The method according to claim 1 wherein the temperature of both the adhering solids being removed and the composition employed to contact and solubilize the solids is maintained at between about l50 F. and 250 F.

5. The method according to claim 3 wherein the CrO is formed in situ in the aqueous H 80, solution by admixing therewith a compound which decomposes therein yielding 00 at the conditions of treatment.

6. The method of claim 1 wherein the solid substances are contacted with the composition for at least about 0.5 hour.

7. The method of claim I wherein the composition comprises 47 percent to 55 percent H 80 and 3.5 percent to 5 percent CrO,

8. The method of claim I wherein the ferrous metal is carbon steel.

l 1 i i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,6 5,816 Dated 26 October 1971 Inventor(s) Theodore E. Majewski and Arthur J. Pastor It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shlown below:

In column 1, line 5, change "difficulty" to difficultly in line 32 change "ficulty" to ficultly in line 38 insert of between "corrosivity" and "nitric" in line +1 delete "nd" and insert and in line hl insert found between "deposits" and "in".

In column 2, line 8, delete "re" and insert more in line 9 delete "solution aqueous solution" and insert an aqueous solution of in line ll insert of between "concentration" and "the"; in line 3' delete "CrO 3" and insert CrO In column 3, change line 19 from "In each six 250milliliter beakers as placed 1 gram each the" to In each of six 250-milliliter beakers was placed L gram of each of the In column l line 26, insert to between "water" and "employ,"

In column 5, line 20, change "difficulty" to difficultly in line 30 insert of between "practice" and 'the"; in line 33 delete "Continued" .n line 53 (the 6th line under Treating Solution in Table V) delete '80% H and insert 80% H SO in line 66 delete "23 8" and insert were Column 6, line 8 (second number in second column of Table VI) hange 25 to 25 .6 in line Sl delete "Cr and insert [110 In column 7, line 2, insert of between "dissolution" and "the"; n line 10 delete "out" and insert Our line 16 change "I to 6" to l to 6 percent in line 19 change "Cro to Cr0 in line 21 elete "ant" and insert amount of In column 8, line I, delete "between abut +0 an" and insert of between about +0 and in line 3 delete "herein and insert wherein n line b delete "aunt" and insert amount J Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR B T T ALK Attesting Officer Commissioner of Patents 

2. The method of claim 1 wherein the Cro3 is present in an amount of between about 3.5 and the point of saturation and the H2SO4 is present in an amount of between about 40 and 57.0 percent.
 3. The method of claim 1 wherein the CrO3 is present in an amount of at least about 3.5 percent and the H2SO4 is present in an amount of between about 47 percent and 55 percent.
 4. The method according to claim 1 wherein the temperature of both the adhering solids being removed and the composition employed to contact and solubilize the solids is maintained at between about 150* F. and 250* F.
 5. The method according to claim 3 wherein the CrO3 is formed in situ in the aqueous H2SO4 solution by admixing therewith a compound which decomposes therein yielding CrO3 at the conditions of treatment.
 6. The method of claim 1 wherein the solid substances are contacted with the composition for at least about 0.5 hour.
 7. The method of claim 1 wherein the composition comprises 47 percent to 55 percent H2SO4 and 3.5 percent to 5 percent CrO3.
 8. The method of claim 1 wherein the ferrous metal is carbon steel. 